Isothermal drying of non-nucleated sugar syrup films

Vigh, S.N., Sheehan, M.E., and Schneider, P.A. (2008) Isothermal drying of non-nucleated sugar syrup films. Journal of Food Engineering, 88 (4). pp. 450-455.

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Abstract

It is important to understand the mechanism of drying from sugar syrup films in order to better control the raw sugar drying process and to correctly design drying equipment. Drying raw sugar involves coupled heat and mass transfer and is complicated by the processes occurring in the syrup film. This study presents isothermal sugar film drying experiments and elucidates the processes occurring in the syrup film by using a simple model based on boiling point elevation. Isothermal drying was achieved in this study by evaporation from a thin film of syrup on a heated plate kept at 40 °C and 58 °C. This study illustrates that the evaporation rate from the film can be reasonably modeled using the plate temperature and the boiling point elevation throughout the entire concentration range up to the glass transition point. The films used in this study were not seeded with crystal and results confirm that crystallisation does not occur by spontaneous nucleation at temperatures above 50 °C and only occurred at lower temperatures when C molasses was used as impurity. Dried films were observed to be hard and glassy. It is assumed that this is amorphous sugar glass and may, on removal of the heat source, reabsorb water. This simplified mechanism for the drying of the syrup film may explain some previously observed anomalous re-hydration behaviour observed for low purity industrial raw sugar.

Item ID: 6590
Item Type: Article (Refereed Research - C1)
Keywords: sugar; film drying; evaporation; modelling; sugar glass; isothermal conditions
ISSN: 1873-5770
Date Deposited: 09 Feb 2010 23:09
FoR Codes: 09 ENGINEERING > 0908 Food Sciences > 090802 Food Engineering @ 100%
SEO Codes: 86 MANUFACTURING > 8601 Processed Food Products and Beverages (excl. Dairy Products) > 860111 Sugar and Confectionery Products @ 50%
97 EXPANDING KNOWLEDGE > 970109 Expanding Knowledge in Engineering @ 50%
Citation Count from Web of Science Web of Science 2
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